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How To Fix Email Error 421



Occasionally, your computer may display an error indicating Email Error 421. There can be multiple causes for this problem.

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SMTP (Simple Mail Transfer Protocol) is an Internet standard for sending e-mail.
SMTP is a text-based protocol in which the sender communicates withSend emails to recipients by entering commands and receiving a response code.


S: 250 Ok

In this example, the client issues the MAIL FROM command and the server respondsfrom 250 approx.

What Is Error 421?

Outlook Error 421 is a common critical SMTP error that prevents e-mail from transferring. The error must be corrected in a timely manner, otherwise it can cause great inconvenience, as all activities associated with your email account will be stopped and blocked. This error occurs when the server has temporary problems sending and receiving email. It can also happen if you have exceeded the limited limit for your email account.

Error 421 SMTP can be displayed in the following formats:

  • “The server responded to with 421 cannot connect to the SMTP server”
  • “An unknown error has occurred: Server error 421”
  • “Your message could not be sent. Error 421 “

Common causes of this critical Outlook 421 error:

  • Configuration errors in Outlook settings are the most common cause. However, this only happens if the email account was recently configured or reconfigured.
  • Problems with firewalls do not cause built-in Windows firewalls. However, firewalls and third-party antivirus programs block connections to specific IP ranges to protect users from spam.
  • Traffic is automatically blocked on port 25 or 26 to prevent users from accessing networks for spam.
  • Failure of VPN connection also causes error 421
  • PST file corruption
  • Viral intervention

  • Download Available To Fully Fix Error 421

    mail error 421

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    Some common causes of this critical Outlook error are:

    • PST memory size exceeds 2GB file size.
    • Incorrect ISP settings.
    • Slow internet connection
    • PST file corruption
  • Trojan horse attack and virus infection
  • This is a critical Outlook error and should be addressed promptly. If you are late it can cause significant inconvenience.

    Error code 421 prevents you from accessing your email account, sending and receiving emails, adding new contacts, viewing emails, mailing records, and more agenda and newspapers. In other words, it will block your email and exclude you from your account.

    To fix this error code on your system, you don’t always need to hire a technician or call network staff to get the job done. This can be a critical bug, but the good news is that it is fairly easy to fix. Even if you don’t have the tech With good knowledge, you can still fix it.

    Here are some of the best practices for solving this problem on your system:



    How do I fix SMTP Error 421?

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    1. Change SMTP settings. Outlook error 421 can be resolved by changing the SMTP settings.
    2. Remove and add your email account.
    3. Change the SMTP port number.
    4. Check for virtual private network (VPN) interference in Outlook.
    5. Try disabling your firewall.

    How do I fix SMTP error?

    Fixed SMTP server error in email
    1. Open your email client (Outlook Express, Outlook, Eudora, or Windows Mail).
    2. On the Tools menu, click Accounts.
    3. Click your email account, then click the Properties button.
    4. Click the General tab.
    5. Make sure the “Email Address” is your valid email address for this account.
    6. Click the Server tab.

    What is SMTP error in Mail?

    Common SMTP Error Codes

    In simple terms, this means that the email could not be delivered. SMTP 550 delivery error can occur for a variety of reasons. Although the 550 error code itself does not say anything about the cause of the error, many SMTP servers contain an explanatory message with an error code.